Method of making a molybdenum alloy having a high titanium content

ABSTRACT

The invention relates to method of making a molybdenum alloy which has a high titanium content and further comprises silicon and/or boron. The method comprises subjecting to pressureless sintering or sintering under pressure in an inert gas atmosphere a mixture of one or more powders (i) of an alloy of Mo and Ti and, optionally, one or more additional metals X and/or (i′) powders of Mo and of TiN, and (ii) one or more powders comprising one or more powders of silicides of Mo and/or Ti and/or (iii) one or more powders of nitrides which comprise Si 3 N 4  powder and/or BN powder.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 ofEuropean Patent Application No. 16193634.9, filed Oct. 13, 2016, theentire disclosure of which is expressly incorporated by referenceherein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method of making a molybdenum alloyhaving a high titanium content which is suitable, for example, for theproduction of structural components, in particular of components,preferably vanes and blades, of turbomachines such as gas turbines andaircraft engines.

2. Discussion of Background Information

Ternary molybdenum alloys are already known which comprise molybdenum,silicon and boron as main alloying constituents. However, when used athigh temperatures, for example in the range from 900° C. to 1300° C.,such alloys do not exhibit sufficient creep resistance. Attempts toincrease the creep resistance with very finely dispersed particles oftitanium, zirconium and carbon, as described, for example, in WO85/03953 A1, the entire disclosure of which is incorporated by referenceherein, have likewise not led to the desired results. Correspondingly,attempts have been made to improve the creep resistance of correspondingalloys using additional alloying elements, such as titanium, zirconium,hafnium, boron, carbon, aluminum, thorium, chromium, manganese, niobium,tantalum, rhenium and tungsten. However, if a corresponding alloy is tobe suitable for the production of structural components and inparticular, components such as vanes and blades of turbomachines whichare used at high temperatures, it must show not only a high creepresistance, but also a good oxidation resistance in the temperaturerange from 900° C. to 1300° C., as well as an adequate static strengthand sufficient ductility.

US 2016/0060734 A1, the entire disclosure of which is incorporated byreference herein, discloses alloys which are suitable for the productionof structural components such as vanes and blades of turbomachines andcomprise molybdenum, silicon, boron and titanium as main components.However, due to the high reactivity of titanium metal with inter alia,oxygen, nitrogen, carbon and hydrogen and its propensity to form stablenon-metallic compounds with these elements corresponding alloys aredifficult and expensive to produce. If titanium is consumed by reactingwith the above elements it is no longer available for the desired phaseformation as Mo—Ti silicide and Mo—Ti mixed crystal. These phases areessential for achieving the properties which are required if the alloyis to be used for manufacturing turbine rotor blades and guide vanes.

In view of the foregoing, it would be advantageous to have available amethod for the production of molybdenum alloys which contain highconcentrations of titanium and are suitable for the production ofstructural components which are subjected to high temperatures and highstress in a relatively simple and cost-efficient manner.

DE 10 2011 013 894 A1, the entire disclosure of which is incorporated byreference herein, discloses a process for the final shape production ofcomponents made of a (titanium-free) material comprising intermetallicphases of trimolybdenum silicide and molybdenum borosilicidehomogeneously distributed in a molybdenum matrix, which processcomprises subjecting a starting powder mixture that comprises at leastmolybdenum (80 mass) and additionally silicon nitride and boron nitrideto a grinding process; producing a suspension with the ground startingpowder mixture that comprises at least an organic binder; introducingthe resulting suspension into a metal powder injection molding tool orconstructing a green body in layers by screen printing; subjecting theplaced green body to thermal and/or chemical treatment for expelling theorganic components; and performing an unpressurized sintering in anon-oxidizing atmosphere or in high-vacuum conditions at 1600° C. Asimilar process is disclosed in US 2009/0011266 A1, the entiredisclosure of which is incorporated by reference herein.

SUMMARY OF THE INVENTION

The present invention provides a method of making a molybdenum alloywhich has a high titanium content and further comprises at least siliconand/or boron. The method comprises subjecting to (pressureless)sintering under vacuum or sintering under pressure in an inert orreducing gas atmosphere (e.g., an Ar/H₂ atmosphere) a mixture of powderswhich comprise (i) one or more powders of an alloy of Mo and Ti and,optionally, one or more additional metals X and/or (i′) powders of Moand of titanium nitride (hereafter TiN) and at least one of (ii) one ormore powders comprising one or more powders of silicides (and preferablyalso borides) of Mo and/or Ti and (iii) one or more powders of nitrideswhich comprise silicon nitride (hereafter Si₃N₄) powder and/or boronnitride (hereafter BN) powder (in particular, at least silicon nitridepowder and preferably both silicon nitride powder and boron nitridepowder).

In one aspect of the method, X, if present in the alloy of Mo and Ti,may be selected from one or more (e.g., one, two, three or more) of Fe,Y, Hf, Nb, Zr and W. For example, at least Fe may be present.

In another aspect of the method, one or more powders (i) (and preferablyno powders (i′)) may be employed. The one or more powders (i) may besubstantially spherical and may have a median particle size d50 (asdetermined by, e.g., laser diffraction) in the range from about 0.001 μmto about 50 μm, e.g., from about 0.001 μm to about 40 μm, or from about0.001 to about 30 μm.

In yet another aspect of the method, one or more powders (i′) (andpreferably no powders (i)) may be employed. The one or more powders (i′)may be substantially spherical and may have a median particle size d50(as determined by, e.g., laser diffraction) in the range from about 0.01μm to about 100 μm, e.g., from about 0.1 μm to about 50 μm, or fromabout 0.01 to about 2 μm.

In a still further aspect of the method, one or more powders (ii) (andpreferably no powders (iii)) may be employed. The one or more silicidepowders (ii) may comprise powders of one or more of MoTi₅Si₃, Ti₅Si₃,MoTi₅SiB₂, Mo₃Si.

In another aspect of the method, one or more powders (iii) (andpreferably no powders (ii)) may be employed. The one or more powders(iii) may comprise one or more powders of silicon nitride and/or one ormore powders of boron nitride. The powders (iii) will often comprise atleast one or more powders of silicon nitride. In other embodiments, bothsilicon nitride powder(s) and boron nitride powder(s) may be employed aspowders (iii).

In another aspect of the method, the powders (i) and/or (i′) and thepowders (ii) and/or (iii) may be combined in ratios which result in analloy which comprises at least 35 at. % of molybdenum and/or not morethan 66 at. % of molybdenum and/or at least 25 at. % of titanium and/ornot more than 33 at. % of titanium and/or at least 9 at. % of siliconand/or not more than 15 at. % of silicon and/or at least 5 at. % ofboron and/or not more than 9 at. % of boron. Preferably, the alloycomprises at least 0.1 at. % of Fe and/or not more than 5 at. % of Fe.

The present invention also provides an alloy which has been obtained bythe method set forth above (including the various aspects thereof), aswell as an article (e.g. a component of a turbine such as a rotor bladeor guide vane) which is made of or comprises this alloy.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The particulars shown herein are by way of example and for purposes ofillustrative discussion of the embodiments of the present invention onlyand are presented in the cause of providing what is believed to be themost useful and readily understood description of the principles andconceptual aspects of the present invention. In this regard, no attemptis made to show details of the present invention in more detail than isnecessary for the fundamental understanding of the present invention,the description making apparent to those of skill in the art how theseveral forms of the present invention may be embodied in practice.

As set forth above, the method provided by the present inventioncomprises subjecting to pressureless sintering or sintering underpressure a mixture of powders which comprise (i) one or more powders ofan alloy of Mo and Ti and, optionally, one or more additional metals X(e.g., one or more of Fe, Y, Hf, Nb, Zr, W and preferably at least Fe)and/or (i′) powders of Mo and of TiN, and further comprise (ii) one ormore powders comprising one or more powders of silicides (and preferablyalso borides) of Mo and/or Ti and/or (iii) one or more powders ofnitrides which comprise Si₃N₄ powder and/or BN powder. Especially incases where powders (iii) are employed in combination with powders (ii),powders (iii) may not comprise Si₃N₄ powder.

The powders (i) may either be purchased (e.g. from H. C. Starck,Germany) or may be prepared, for example, by atomization in an inert gasatmosphere (preferably high purity argon) of a block or ingot of analloy of Mo, Ti and, optionally, X to obtain a powder with particleswhich will usually be substantially spherical and will have a particlesize (longest dimension and/or diameter) of less than 45 μm (e.g., lessthan 10 μm, or less than 1 μm). The alloy can be prepared, for example,by melting together (e.g., by plasma melting or arc melting) powders ofmetallic Mo, Ti and optionally one or more metals X and/or correspondingpre-alloys such as, e.g., Mo₈₀Ti₂₀, Mo₇₀Ti₃₀, Mo₆₀Ti₄₀, etc. (e.g., inpowder form). Powders (i′) may be prepared, for example, by reducingmolybdenum oxides with e.g., hydrogen and by nitriding Ti powder,respectively. In this regard it is to be noted that the phrase “lessthan z μm” as used herein is intended to mean that at least 95% byweight, e.g., at least 98% by weight, or at least 99% by weight of theparticles have a longest dimension or diameter of z μm. The particlesize can be determined by methods well known to those of skill in theart, for example by sieve analysis or optical methods such as laserdiffraction.

The atomization of an ingot or block may, for example, be carried out byan EIGA (Electrode Induction melting Gas Atomization) process or by gasatomization using a Laval nozzle (preferably using high purity argon).The atomization may optionally be preceded by subjecting the alloyobtained by, e.g., arc melting or plasma melting to hot isostaticpressing (HIP), e.g., at a temperature of from about 1,300° C. to about1,500° C. and at a pressure of from about 100 to about 300 MPa for about5 to about 10 hours. Prior to and/or after the hot isostatic pressing aheat treatment may be carried out, e.g., at a temperature of from about1,300° C. to about 1,600° C. for about 5 to about 50 hours.

Non-limiting examples of commercially available powders (i) for use inthe instant method have a median particle size d50 in the range fromabout 0.01 μm to about 50 μm (at a purity of, e.g., from about 95% toabout 99.9% by weight) or a d50 of from about 0.01 μm to about 30 μm (ata purity of, e.g., from about 98% to about 99.9% by weight).

The alloy of Mo, Ti and, optionally, X for making the one or morepowders (i) may, for example, comprise (in % by weight based on thetotal weight of the alloy):

Mo from about 55 to about 95, e.g. from about 60 to about 85

Ti from about 10 to about 30, e.g. from about 15 to about 25

Fe from 0 to about 3, e.g. from about 1 to about 2

Nb from 0 to about 30, e.g. from about 10 to about 20

Zr from 0 to about 10, e.g. from about 2 to about 4

W from 0 to about 20, e.g. from about 4 to about 10

Hf from 0 to about 3, e.g. from about 1 to about 2

Y from 0 to about 3, e.g. from about 1 to about 2.

If present, one, two, three, four, five or all of Fe, Nb, Zr, W, Hf andY may be present in the alloy.

The alloy for making the one or more powders (i) preferably does notcontain any (or at most only trace amounts) of Si and B because thepresence of these elements will cause the alloy to become brittle. Thesame applies to the one or more powders (i′).

Non-limiting examples of commercially available Mo powders (i′) for usein the instant method have a median particle size d50 in the range fromabout 0.1 μm to about 50 μm (at a purity of, e.g., from about 95% toabout 99.9% by weight) or a d50 of from about 0.5 μm to about 2 μm (at apurity of, e.g., from about 98% to about 99.9% by weight). The sameapplies to TiN powders.

The one or more powders (ii) for use in the instant method may comprisepowders of one or more of Mo(Ti)₅Si₃, Ti₅Si₃, Mo(Ti)₅SiB₂, Mo₃Si. Theone or more powders (ii) may either be purchased (e.g., from H. C.Starck, Germany) or may be prepared by, for example, arc melting(usually in an argon atmosphere) from elemental Mo, Ti and Si (andpreferably B), usually in the form of powders of the elements and/orcorresponding pre-alloys. The powders (ii) will usually comprise one ormore phases of formula MoTi₅Si₃, Ti₅Si₃, MoTi, and MoTi₅SiB₂ and/orcorresponding substoichiometric or hyperstoichometric phases. Forexample, these phases may contain more or less Si and/or B thanindicated, or may contain Mo and/or Ti, which can activate the sinteringprocess and can result in high sinter densities (e.g., >95%).

The powders (ii) for use in the instant method will usually have amedian particle size d50 (as determined by, e.g., laser diffraction) inthe range from about 0.001 μm to about 50 μm, e.g., from about 0.001 μmto about 40 μm, or from about 0.001 to about 30 μm.

Non-limiting examples of commercially available powders (ii) for use inthe instant method may have a median particle size d50 as follows:

-   Mo₃Si from about 10 μm to about 30 μm (at a purity of, e.g., from    about 98% to about 99.99% by weight) or from about 1 μm to about 10    μm (at a purity of, e.g., from about 99% to about 99.9% by weight)-   Ti₅Si₃ from about 10 μm to about 30 μm (at a purity of, e.g., from    about 98% to about 99.9% by weight)-   Mo(Ti)₅Si₃ from about 0.01 μm to about 50 μm (at a purity of, e.g.,    from about 98% to about 99.99% by weight) or from about 0.01 μm to    about 30 μm (at a purity of, e.g., from about 99% to about 99.9% by    weight)-   Mo(Ti)₅SiB₂ from about 0.01 μm to about 50 μm (at a purity of, e.g.,    from about 98% to about 99.99% by weight) or from about 0.01 μm to    about 30 μm (at a purity of, e.g., from about 99% to about 99.9% by    weight).

The one or more powders (iii) which may be used in combination with orinstead of the one or more powders (ii) are readily commerciallyavailable (e.g., from H. C. Starck, Germany).

The powders (iii) for use in the instant method will usually have amedian particle size d50 (as determined by, e.g., laser diffraction) inthe range from about 0.001 μm to about 50 μm, e.g., from about 0.001 μmto about 40 μm, or from about 0.001 to about 30 μm.

Non-limiting examples of commercially available powders (iii) for use inthe instant method may have a median particle size d50 as follows:

-   Si₃N₄ from about 0.1 μm to about 5 μm (at a purity of, e.g., from    about 95% to about 99.9% by weight) or from about 0.5 μm to about 1    μm (at a purity of, e.g., from about 98% to about 99.9% by weight)-   BN from about 0.1 μm to about 5 μm (at a purity of, e.g., from about    95% to about 99.9% by weight) or from about 0.5 μm to about 1 μm (at    a purity of, e.g., from about 98% to about 99.9% by weight).

The powders (i) and/or (i′) and the powders (ii) and/or (iii) are mixedand optionally milled, and then subjected to a sintering process (eitherpressureless or under pressure in a reducing or inert gas atmosphere,e.g., an atmosphere consisting essentially of Ar/H₂ or helium).Corresponding processes are well known to those of skill in the art.Prior to sintering the mixed (and optionally milled) powders willusually be combined with a preferably organic binder (e.g., an organicwax) and then subjected to cold isostatic pressing (CIP) at roomtemperature, e.g., at a pressure of from about 100 to about 300 MPa for,e.g., about 5 to about 60 minutes, to form a green body.

The one or more powders (i) or (i′) are usually mixed with the one ormore powders (ii) and/or (iii) in ratios which result in a weightpercentage of the one or more powders (i) and/or the one or more powders(i′) of at least about 85%, e.g., at least about 88%, at least about90%, at least about 92%, or at least about 94% by weight, but usuallynot higher than about 97%, e.g., not higher than about 96% by weight,based on the total weight of the powder mixture (i.e., without optionalbinder). Merely by way of example, weight percentages of powders (i) and(iii) in a corresponding mixture may be as follows:

Powder (i) from about 85 to about 97, e.g., from about 92 to about 96

Si₃N₄ from about 2 to about 15, e.g., from about 3 to about 7

BN from about 0.5 to about 5, e.g., from about 1 to about 3.

The sintering (or reaction sintering if nitrides are present) is usuallycarried out in several (e.g., two, three or four) steps at differenttemperatures. Merely by way of example, the sintering may be carriedout, in each case with a holding time of from about 1 to about 3 hours,(1) at a temperature of from about 350° C. to about 450° C. (e.g., atabout 400° C.) to decompose the optionally present organic binder, (2)at a temperature of from about 650° C. to about 750° C. (e.g., at about700° C.) to decompose nitrides, if present, (3) at a temperature of fromabout 1,150° C. to about 1,250° C. (e.g., at about 1,200° C.) and (4) ata temperature of from about 1,650° C. to about 1,750° C. (e.g., at about1,700° C.).

The sintered body thus obtained may optionally be subjected to hotisostatic pressing (HIP), e.g., at a temperature of from about 1,300° C.to about 1,500° C. and at a pressure of from about 100 to about 300 MPafor about 5 to about 10 hours. Prior to and/or after the HIP a heattreatment may be carried out, e.g., at a temperature of from about1,300° C. to about 1,600° C. for about 5 to about 50 hours.

The sintered body may also be subjected to forming (optionally precededby HIP and/or heat treatment(s) as set forth above) such as, e.g.,rolling, extrusion, forging (e.g., isothermal or “hot die”), optionallyfollowed by a heat treatment as set forth above.

It should also be noted that in the case of the absence of nitrides inthe powder mixture the sintering (and the CIP) can be replaced by agenerative production method, e.g. by using a laser with which a desiredstructure is built up layer by layer, the laser being used to sintereach deposited layer of powder material before the next layer of powdermaterial is deposited.

The following embodiments of the instant method are provided for purelyillustrative purposes.

Embodiment 1

A powder (i) was prepared by arc melting of a powder mixture ofelemental Mo (81% by weight), Ti (18% by weight) and Fe (1% by weight)to form an ingot, followed by atomization of the ingot by means of aLaval nozzle. The powder (i) (93% by weight based on powder mixture) wasthen mixed with powders (iii) of Si₃N₄ (5% by weight) and BN (2% byweight) in a planetary ball mill (mass ratio balls:powder=10:1, 100rev/min) for 15 minutes and the resultant mixture was combined with anorganic binder (e.g., wax) and then subjected to CIP for about 10minutes at about 300 MPa and thereafter to reaction sintering at about400° C. for about 1 hour in an Ar/H₂ atmosphere, about 700° C. for about1 hour in an Ar/H₂ atmosphere, about 1,200° C. for about 1 hour invacuum and about 1,700° C. for about 1 hour in vacuum, followed by aheat treatment at about 1,400° C. for about 10 hours and HIP for about 5hours at about 1,400° C. and about 150 MPa. The resultant product showedthe following (approximate) concentrations (in at. %):

Mo 57

Ti 25

Fe 1

Si 9

B 8

Embodiment 2

A powder (i) is prepared by plasma melting of a powder mixture ofelemental Mo, Ti, Fe and Hf to form an ingot, followed by atomization ofthe ingot by means of a Laval nozzle. The powder (i) is then mixed withpowders (iii) of Si₃N₄ and BN and an organic binder and the resultantmixture is subjected to CIP and thereafter to reaction sintering attemperatures of about 400° C., about 700° C., about 1,200° C. and about1,700° C., each for about 1-3 hours in a reducing atmosphere or invacuum, followed by a heat treatment at about 1,400° C. for about 10hours and HIP for about 5 hours at about 1,400° C. and about 150 MPa.

Embodiment 3

A powder (i) is prepared by are melting or plasma melting of a powdermixture of elemental Mo, Ti, Fe, Y, Hf, Nb, Zr and W to form an ingot,followed by an optional heat treatment, optional HIP and atomization ofthe ingot by means of a Laval nozzle or by means of an EIGA method. Thepowder (i) is then mixed with powders (iii) of Si₃N₄ and BN and anorganic binder and the resultant mixture is subjected to CIP andthereafter to reaction sintering at temperatures of about 400° C., about700° C., about 1,200° C. and about 1,700° C., each for about 1-3 hoursin a reducing atmosphere or in vacuum, followed by optional HIP forabout 5 to about 10 hours at a temperature of from about 1,300° C. toabout 1,500° C. and a pressure of from about 100 to about 300 MPa,forming by rolling, extrusion or forging at a temperature of higher than1,600° C. and a subsequent heat treatment for about 5 to about 50 hoursat a temperature of from about 1,300° C. to about 1,600° C.

Embodiment 4

A powder (i) is prepared by plasma melting of a powder mixture ofelemental Mo, Ti and Fe to form an ingot, followed by atomization of theingot by means of a Laval nozzle. The powder (i) is then mixed withpowders (ii) of Mo(Ti)₅Si₃ and Mo(Ti)₅SiB₂ and an organic binder and theresultant mixture is subjected to CIP and thereafter to sintering attemperatures of about 400° C., about 1,200° C. and about 1,700° C., eachfor about 1-3 hours in a reducing atmosphere or in vacuum, followed by aheat treatment at about 1,400° C. for about 10 hours and HIP for about 5hours at about 1,400° C. and about 150 MPa.

Embodiment 5

A powder mixture (i′) of elemental Mo and of TiN is mixed with powders(iii) of Si₃N₄ and BN and an organic binder and the resultant mixture issubjected to CIP and thereafter to reaction sintering at temperatures ofabout 400° C., about 700° C., about 1,200° C. and about 1,700° C., eachfor about 1-3 hours in a reducing atmosphere or in vacuum, followed by aheat treatment at about 1,400° C. for about 10 hours and HIP for about 5hours at about 1,400° C. and about 150 MPa.

As set forth above, the method of the present invention is suitable formaking molybdenum alloys which have a high titanium content. The term“molybdenum alloy” as used herein and in the appended claims refers toan alloy in which the element molybdenum makes up the greatest alloyingfraction in at. %. In other words, in a molybdenum alloy, there is noother element which has a greater alloying fraction in at. % than Mo.The molybdenum content of the alloy in at. % will usually be at least 30at. %, preferably at least 35 at. %, and in particular at least 40 at.%, e.g., at least 45 at. % (based on all elements present in the alloy,as in the following).

“High titanium content” as used herein and in the appended claims refersto a titanium content of at least 15 at. %, preferably at least 20 at. %and particularly at least 25 at. %, e.g., at least 30 at. %.

In one aspect, the alloy made by the instant method may further compriseiron and/or yttrium, each in a concentration of from 0.1 to 5 at. %, inparticular in a concentration of from 0.3 to 3 at. %. For example, ironmay be present in a concentration of from 0.5 to 3 at. %, e.g., from 0.8to 2 at. %, and/or yttrium may be present in a concentration of from 0.3to 3 at. %, e.g., from 0.5 to 2 at. %.

The alloy produced by the method of the present invention may furthercomprise one or more of zirconium, niobium, hafnium, and tungsten. Forexample, zirconium may be present in a concentration of not more than 5at. %, e.g., in a concentration of from 0.3 to 3 at. %, and/or niobiummay be present in a concentration of not more than 20 at. %, e.g., in aconcentration of from 0.3 to 10 at. %, and/or tungsten may be present ina concentration of not more than 8 at. %, e.g., in a concentration offrom 0.3 to 5 at. % and/or hafnium may be present in a concentration ofnot more than 5 at. %, e.g., in a concentration of from 0.3 to 3 at. %.

The alloy of the present invention may comprise silicon in aconcentration of from 9 to 15 at. %, e.g., in a concentration of from 12to 14 at. %, and/or boron in a concentration of from 5 to 9 at. %, e.g.,in a concentration of from 5 to 6 at. %, and/or titanium in aconcentration of from 25 to 33 at. %, e.g., in a concentration of from26 to 29 at. %.

The alloy may, for example, be formed exclusively of molybdenum,silicon, boron, titanium, iron, yttrium, niobium, tungsten, zirconium,hafnium (and unavoidable impurities), or may be formed exclusively ofmolybdenum, silicon, boron, titanium, iron, yttrium (or hafnium).

In another aspect of the alloy, molybdenum may be present in aconcentration of from 35 to 66 at. %, e.g., in a concentration of from40 to 60 at. %, or from 45 to 57 at. %, or in a concentration such thatthe alloy comprises 100 at. % together with the remaining alloyingconstituents mentioned.

In another aspect, the true density of the produced alloy may be lessthan or equal to 9 g/cm³, e.g., less than or equal to 8.5 g/cm³, or lessthan or equal to 8 g/cm³.

In yet another aspect, the structure of the alloy may comprise a matrixof a molybdenum mixed crystal and silicide phases, the silicide phasesbeing formed in particular by Mo(Ti)₅Si₃ and/or Mo(Ti)₅SiB₂. Forexample, the alloy may comprise from about 15 to about 35 vol. %, e.g.,from about 25 to about 35 vol. % Mo(Ti)₅Si₃ and from about 15 to about35 vol. %, e.g., from about 15 to about 25 vol. % Mo(Ti)₅SiB₂ and fromabout 1 to about 20 vol. % minor phases. Also by way of example, thealloy may comprise from about 45 to about 55 vol. %, e.g., from about 48to about 55 vol. %, molybdenum mixed crystal or a fraction of molybdenummixed crystal such that the alloy together with the remaining phaseconstituents comprises 100 vol. %.

As minor alloying constituents, one or both of niobium and tungsten mayadditionally be present in the alloy. The addition of niobium improvesthe fracture toughness and therefore the deformability or ductility,whereas tungsten improves the oxidation resistance of the alloy.

Preferably, the alloy is formed exclusively of the elements molybdenum,silicon, boron, titanium, iron, yttrium, niobium, tungsten, hafnium andzirconium, wherein the fraction of niobium, tungsten, hafnium andzirconium may be 0 at. %. As is known to those skilled in the art, analloy can comprise further elements as unavoidable impurities, wherein,however, none of these further elements should make up more than 1 at.%, preferably more than 0.1 at. %, in the alloy.

With the main and minor alloying elements, therefore, alloys can beproduced by the method of the present invention which, in addition tounavoidable impurities, exclusively comprise Mo, Si, B, Ti, Fe, Y, Zr,Nb, Hf and/or W. In particular, Mo—Si—B—Ti—Fe—, Mo—Si—B—Ti—Fe—Zr—,Mo—Si—B—Ti—Fe—Y—, Mo—Si—B—Ti—Fe—Y—Nb— and Mo—Si—B—Ti—Fe—Y—Nb—W alloyscan be produced, likewise a Mo—Si—B—Ti—Y alloy which does not compriseiron, although an alloy containing iron is preferred in principle.

The alloy composition can in particular also be selected in such amanner that the true density, that is to say the density without anypores or cavities, is adjusted to be less than or equal to 9 g/cm³,e.g., less than or equal to 8.5 g/cm³, or less than or equal to 8 g/cm³.

The corresponding structure of the alloy can be adjusted in such amanner that the structure has a matrix of molybdenum mixed crystal(e.g., molybdenum-titanium mixed crystal), into which the silicidephases are incorporated, wherein the silicide phases can be formed byMo(Ti)₅Si₃ and/or Mo(Ti)₅SiB₂. In the respective silicides, therefore,molybdenum can be replaced by titanium and vice versa.

The molybdenum alloy made by the method of the present invention maycomprise from 15 to 35 vol. %, e.g., from 25 to 35 vol. % Mo(Ti)₅Si₃ andfrom 15 to 35 vol. %, e.g., from 15 to 25 vol. % Mo(Ti)₅SiB₂ and from 1to 20 vol. %, e.g., from 1 to 5 vol. %, minor phases. Minor phases cancomprise various phases, in particular various mixed phases or mixedcrystals of the alloying elements present in the alloy.

The molybdenum alloy may additionally comprise from about 45 to about 55vol. %, e.g., from about 48 to about 55 vol. %, molybdenum mixed crystalor a fraction of molybdenum mixed crystal such that the alloy togetherwith the remaining phase constituents comprises 100 vol. %.

With a corresponding molybdenum alloy, in particular components ofturbomachines, preferably of gas turbines or aero engines can bemanufactured, wherein the components can be, in particular, rotor bladesor guide vanes of the turbomachine, and in particular guide vanes orrotor vanes of rapidly running uncooled low-pressure turbines.

Advantageous properties having a balanced property profile with respectto creep resistance, static strength, fracture toughness, ductility,oxidation resistance and low specific gravity have been achieved withthe following exemplary alloy compositions (figures in each case in at.%), which can also comprise small amounts of further elements asunavoidable impurities:

Mo Si B Ti Fe Y Zr Nb W Hf 49.5 12.5 8.5 27.5 2.0 0 0 0 0 0 48.5 13.58.5 26.5 2.0 0 1.0 0 0 0 51.0 10.0 8.5 27.5 2.0 0 1.0 0 0 0 46.5 12.58.5 27.5 2.0 2.0 1.0 0 0 0 46.5 12.5 8.5 27.5 2.0 2.0 0 1.0 0 0 46.512.5 8.5 27.5 2.0 2.0 0 0 1.0 0 49.3 13.5 5.5 27.5 1.2 0 0 0 1.0 0 50.513.5 5.5 27.5 2.0 0 0 0 0 1.0 53.0 13.5 5.5 27.0 1.0 0 0 0 0 0 51.0 13.55.5 27.0 1.0 0 0 0 0 2.0 46.0 13.5 5.5 27.0 1.0 0 0 5.0 0 2.0

Although the present invention has been described herein with referenceto particular means, materials and embodiments, the present invention isnot intended to be limited to the particulars disclosed herein; rather,the present invention extends to all functionally equivalent structures,methods and uses, such as are within the scope of the appended claims.

What is claimed is:
 1. A method of making a molybdenum alloy having ahigh titanium content and further comprising one or both of silicon andboron, wherein the method comprises subjecting to pressureless sinteringor sintering under pressure a mixture of powders which comprise (i) oneor more powders of an alloy of Mo and Ti and, optionally, one or moreadditional metals X and/or (i′) powders of Mo and of titanium nitride,and at least one of (ii) one or more powders comprising one or morepowders of silicides of Mo and/or Ti and (iii) one or more powders ofnitrides which comprise at least one of silicon nitride and boronnitride.
 2. The method of claim 1, wherein X is present and selectedfrom one or more of Fe, Y, Hf, Nb, Zr, W.
 3. The method of claim 2,wherein the one or more metals X comprises at least Fe.
 4. The method ofclaim 1, wherein one or more powders (i) are employed.
 5. The method ofclaim 4, wherein the one or more powders (i) have a median particle sized50 of from about 0.001 μm to about 50 μm.
 6. The method of claim 1,wherein the particles of (i) are substantially spherical.
 7. The methodof claim 1, wherein one or more powders (ii) are employed.
 8. The methodof claim 7, wherein the one or more powders (ii) comprise powders of oneor more of MoTi₅Si₃, Ti₅Si₃, MoTi₅SiB₂, Mo₃Si.
 9. The method of claim 1,wherein one or more powders (iii) are employed.
 10. The method of claim9, wherein the one or more powders (iii) comprise at least siliconnitride powder.
 11. The method of claim 1, wherein one or more powders(i′) are employed.
 12. The method of claim 11, wherein the one or morepowders (i′) have a median particle size d50 of from about 0.001 μm toabout 50 μm.
 13. The method of claim 1, wherein the powders (i) and/or(i′) and the powders (ii) and/or (iii) are combined in ratios whichresult in an alloy which comprises at least 35 at. % of molybdenum. 14.The method of claim 13, wherein the powders (i) and/or (i′) and thepowders (ii) and/or (iii) are combined in ratios which result in analloy which comprises not more than 66 at. % of molybdenum.
 15. Themethod of claim 1, wherein the powders (i) and/or (i′) and the powders(ii) and/or (iii) are combined in ratios which result in an alloy whichcomprises at least 25 at. % of titanium.
 16. The method of claim 15,wherein the powders (i) and/or (i′) and the powders (ii) and/or (iii)are combined in ratios which result in an alloy which comprises not morethan 33 at. % of titanium.
 17. The method of claim 1, wherein thepowders (i) and/or (i′) and the powders (ii) and/or (iii) are combinedin ratios which result in an alloy which comprises at least 9 at. % ofsilicon.
 18. The method of claim 17, wherein the powders (i) and/or (i′)and the powders (ii) and/or (iii) are combined in ratios which result inan alloy which comprises not more than 15 at. % of silicon.
 19. An alloywhich is obtained by the method of claim
 1. 20. An article which is madeof or comprises the alloy of claim 19.